Human T-cell lymphotropic virus I (HTLV-I) is the etiological agent for Adult T-cell Leukemia (ATL). Past studies have provided evidence that deregulation of IL-2 receptor signaling may play an important role in the events that lead to immortalization and oncogenic transformation of CD4+ T-cells by HTLV-1. Indeed, constitutive activation of the IL-2R complex including the Jak/STAT pathway is found in HTLV-1 transformed cells and freshly isolated leukemic cells from ATL patients. We and others have recently demonstrated that Shp-1, a constitutively expressed cytosolic protein tyrosine phosphatase that functions as an early negative regulator of IL-2R signaling is selectively and markedly downregulated in HTLV-1 transformed cells. Shp-1 is normally recruited to phosphorylated docking sites on IL-2R where it can then dephosphorylate activated protein tyrosine (Jak) kinases that are part of the signaling complex and we hypothesize that SHP-1 downregulation is of central importance to HTLV-1 leukemogenesis. In this proposal we provide new data which demonstrates by ChIP assay analysis that both the histone deacetylase HDAC1, the histone H3 methyl transferase SUV39H1 and HTLV-1 Tax are bound to the Shp-1 promoter in the HTLV-1 transformed cells. Thus, the molecular basis of Shp-1 promoter silencing appears to be the assembly of a repressor complex involving HDAC1, SUV39H1 and Tax and other unknown proteins at the Shp-1 promoter. In this proposal we will investigate the molecular basis of Shp-1 promoter silencing in these HTLV-1 transformed cells. Specifically, we will first identify and map the core promoter region and transcription factor binding sites in the Shp-1 promoter and determine if transcription factor binding is altered in HTLV-1 transformed and ATL cell lines. We will also determine by ChIP assay if there is binding of transcriptional repressors, methyl-cytosine binding proteins or various chromatin-remodeling complexes to the Shp-1 promoter in the HTLV-1 transformed cell lines. We will also determine if the Shp-1 core promoter region has been methylated. We will also identify the "histone code" of the Shp-1 promoter in fresh CD4+ T-cells and non-HTLV-1 transformed cells and compare this code to HTLV-1 transformed and ATL cell lines. By comparing these codes to the Shp-1 mRNA and protein expression profiles in these cells we will determine if the precise histone codes for Shp-1 expression and silencing can be identified. We will correlate these findings to the ChIP assay analyses of chromatin modifying proteins to determine if the biochemical mechanisms involved in Shp-1 promoter silencing can be elucidated. We will also determine the molecular interactions that lead to HTLV-1 Tax binding to the Shp-1 promoter and will evaluate post-translational modifications to Tax (e.g. acetylation, methylation) that may influence preferential binding to transcription factors, coactivators or corepressors. Finally, we will examine the effects of inhibitors of histone deacetylase and DNA methyltransferase on activation of the Shp-1 promoter in HTLV-1 transformed cell lines. We will also investigate the biological consequences of this inhibition on Shp-1 expression and constitutive activation of the Jak/STAT pathway. These studies will be coupled with Shp-1 gene replacement studies to evaluate the longer term consequences of Shp-1 re-expression on cell proliferation, viability, cell cycle progression and apoptosis. These studies should provide new insight into the biochemical mechanisms of HTLV-1 leukemogenesis and aid in the development of new treatments for this fatal disease.